Improved online current-error boundary computation for switching frequency variation control in hysteresis controlled VSI-Fed IM drives

This paper proposes an improved control strategy for switching frequency variation in hysteresis current controlled Voltage Source Inverter (VSI) fed induction motor drives. The advantages of simple hysteresis controller, viz. simple implementation and fast dynamic response are added with the advantages of constant switching frequency and reduction in switching losses and harmonic distortion in the proposed controller. Elimination of look up tables is possible since boundary computation is performed online with estimated stator voltages calculated using current errors along the orthogonal axes thus making implementation easier. The voltage vector to be switched in the next sampling interval is identified by the boundary computed in the present sampling interval. The vector selection logic is designed to extract the features of continual- clamp VC-SVPWM based VSI fed IM drive whereby reduced harmonic distortion at higher modulation indices and reduction in switching losses are obtained. A comparative simulation study of the current error space phasor based controller resembling the characteristics of conventional VC-SVPWM based drive with the proposed controller based drive has been conducted using SIMULINK toolbox of MATLAB for steady state as well as transient performance analysis.